1. Field of the Invention
The present invention relates to a numerically controlled reversible gear system for removing the backlash in all the driving stages, i.e. at stopping, forward running, backward running and for improving accuracy of the stopping position so as to decrease an error caused by the angular deviation of the system.
2. Description of the Prior Art
A numerical controlled equipment is generally controlled by output pulses delivered from a control equipment and for instance the pulses are supplied to necessary servo motors such as an X direction servo motor and a Y direction servo motor according to a predetermined program and an output head is driven in a desired pattern determined by the program. In the conventional driving systems, there is a certain mechanical play due to the mechanism at a switching between a forward running and a backward running. Accordingly, for instance, if 10 pulse backward running is instructed after an instruction of 10 pulse forward running from an original position, the output head may not return to the original position correctly and thus the stopping position shows a certain deviation. This deviation is termed as "backlash" and various measures have been considered for compensating the same. The hitherto known backlash compensating apparatus of the numerical controlled machining equipment are generally of very complicated mechanism and have difficulties in view of their compensation accuracies despite their high cost.
The problems of the conventional numerical controlled equipment may be summerized in more detail below.
1. The amount of backlash is an analog amount, whereas the automatic compensation of the backlash is generally effected by a digital amount so that a perfect compensation is difficult. PA1 2. The automatic backlash compensation is effected only at a time of switiching the driving direction so that a backlash produced during in either directional rotation or in stopping condition can not be removed. PA1 3. When the rotation of the pulse motor is stopped, moving parts of the equipment may stop at a position having a certain deviation within the range of the backlash of the gear system by the moment of inertia of the moving parts or in a range added with an error of angular deviation thereto so that the accuracy of the stopping position may decrease accordingly. PA1 4. When a rotation instruction is given to the pulse motor, an angular deviation error may produce due to static and dynamic characteristics inherent to the pulse motor itself, and by the presence of friction, torque and moment of inertia of the mechanical systems. Therefore, there will be a case that the rotational instruction pulses less than a certain number of few pulses are not sufficient to properly drive the system. PA1 5. An automatic backlash compensation device generally becomes complicated and hence it becomes costly and it may cause many troubles during the operation. PA1 a. The backlash may substantially be removed in all stages of the operations, e.e. stopping, forward rotation, and backward rotation. PA1 b. The inertia of movement may be suppressed even in case of a sudden stop and hence the accuracy of the stopping position may greatly be improved. PA1 c. The equipment may sufficiently respond to repeated single pulse instruction of forward rotation and backward rotation. PA1 d. An arithmetically procesing automatic apparatus for the backlash may completely be dispensed with. PA1 e. The equipment may be assembled in simple and inexpensive manner.